Dinoflagellate symbiosis: strategies and adaptations for the aquisition and fixation of inorganic carbon

Dinoflagellates exist in symbiosis with a number of marine invertebrates including giant clams, which are the largest of these symbiotic organisms. The dinoflagellates (Symbiodinium sp.) live intercellularly within tubules in the mantle of the host clam. The transport of inorganic carbon (Ci) from seawater to Symbiodinium (=zooxanthellae) is an essential function of hosts that derive the majority of their respiratory energy from the photosynthate exported by the zooxanthellae. Immunolocalisation studies show that the host has adapted its physiology to acquire, rather than remove CO2, from the haemolymph and clam tissues. Two carbonic anhydrase (CA) isoforms (32 and 70 kDa) play an essential part in this process. These have been localised to the mantle and gill tissues where they catalyse the interconversion of HCO3- to CO2, which then diffuses into the host tissues. The zooxanthellae exhibit a number of strategies to maximise Ci acquisition and utilisation. This is necessary as they express a form II Rubisco that has poor discrimination between CO2 and O-2. Evidence is presented for a carbon concentrating mechanism (CCM) to overcome. this disadvantage. The CCM incorporates the presence of a light-activated CA activity, a capacity to take up both HCO3- and CO2, an ability to accumulate an elevated concentration of Ci within the algal cell, and localisation of Rubisco to the pyrenoid. These algae also express both external and intracellular CAs, with the intracellular isoforms being localised to the thylakoid lumen and pyrenoid. These results have been incorporated into a model that explains the transport of Ci from seawater through the clam to the zooxanthellae.

Study on diffusion and flow of benzene, n-hexane and CCl4 in activated carbon by a differential permeation method

In this paper the diffusion and flow of carbon tetrachloride, benzene and n-hexane through a commercial activated carbon is studied by a differential permeation method. The range of pressure is covered from very low pressure to a pressure range where significant capillary condensation occurs. Helium as a non-adsorbing gas is used to determine the characteristics of the porous medium. For adsorbing gases and vapors, the motion of adsorbed molecules in small pores gives rise to a sharp increase in permeability at very low pressures. The interplay between a decreasing behavior in permeability due to the saturation of small pores with adsorbed molecules and an increasing behavior due to viscous flow in larger pores with pressure could lead to a minimum in the plot of total permeability versus pressure. This phenomenon is observed for n-hexane at 30degreesC. At relative pressure of 0.1-0.8 where the gaseous viscous flow dominates, the permeability is a linear function of pressure. Since activated carbon has a wide pore size distribution, the mobility mechanism of these adsorbed molecules is different from pore to pore. In very small pores where adsorbate molecules fill the pore the permeability decreases with an increase in pressure, while in intermediate pores the permeability of such transport increases with pressure due to the increasing build-up of layers of adsorbed molecules. For even larger pores, the transport is mostly due to diffusion and flow of free molecules, which gives rise to linear permeability with respect to pressure. (C) 2002 Elsevier Science Ltd. All rights reserved.

Adsorption of mixtures containing subcritical fluids on activated carbon

A theoretical analysis of adsorption of mixtures containing subcritical adsorbates into activated carbon is presented as an extension to the theory for pure component developed earlier by Do and coworkers. In this theory, adsorption of mixtures in a pore follows a two-stage process, similar to that for pure component systems. The first stage is the layering of molecules on the surface, with the behavior of the second and higher layers resembling to that of vapor-liquid equilibrium. The second stage is the pore-filling process when the remaining pore width is small enough and the pressure is high enough to promote the pore filling with liquid mixture having the same compositions as those of the outermost molecular layer just prior to pore filling. The Kelvin equation is applied for mixtures, with the vapor pressure term being replaced by the equilibrium pressure at the compositions of the outermost layer of the liquid film. Simulations are detailed to illustrate the effects of various parameters, and the theory is tested with a number of experimental data on mixture. The predictions were very satisfactory.

Sequencing batch reactor technology: the key to a BP refinery (Bulwer Island) upgraded environmental protection system - a low cost lagoon based retro-fit

BP Refinery (Bulwer Island) Ltd (BP) located on the eastern Australian coast is currently undergoing a major expansion as a part of the Queensland Clean Fuels Project. The associated wastewater treatment plant upgrade will provide a better quality of treated effluent than is currently possible with the existing infrastructure, and which will be of a sufficiently high standard to meet not only the requirements of imposed environmental legislation but also BP's environmental objectives. A number of challenges were faced when considering the upgrade, particularly; cost constraints and limited plot space, highly variable wastewater, toxicity issues, and limited available hydraulic head. Sequencing Batch Reactor (SBR) Technology was chosen for the lagoon upgrade based on the following; SBR technology allowed a retro-fit of the existing earthen lagoon without the need for any additional substantial concrete structures, a dual lagoon system allowed partial treatment of wastewaters during construction, SBRs give substantial process flexibility, SBRs have the ability to easily modify process parameters without any physical modifications, and significant cost benefits. This paper presents the background to this application, an outline of laboratory studies carried out on the wastewater and details the full scale design issues and methods for providing a cost effective, efficient treatment system using the existing lagoon system.

Combining nonthermal technologies to control foodborne microorganisms

Novel nonthermal processes, such as high hydrostatic pressure (HHP), pulsed electric fields (PEFs), ionizing radiation and ultrasonication, are able to inactivate microorganisms at ambient or sublethal temperatures. Many of these processes require very high treatment intensities, however, to achieve adequate microbial destruction in low-acid foods. Combining nonthermal processes with conventional preservation methods enhances their antimicrobial effect so that lower process intensities can be used. Combining two or more nonthermal processes can also enhance microbial inactivation and allow the use of lower individual treatment intensities. For conventional preservation treatments, optimal microbial control is achieved through the hurdle concept, with synergistic effects resulting from different components of the microbial cell being targeted simultaneously. The mechanisms of inactivation by nonthermal processes are still unclear; thus, the bases of synergistic combinations remain speculative. This paper reviews literature on the antimicrobial efficiencies of nonthermal processes combined with conventional and novel nonthermal technologies. Where possible, the proposed mechanisms of synergy is mentioned. (C) 2003 Elsevier Science B.V. All rights reserved.

SPAnDX: a process-based population dynamics model to explore management and climate change impacts on an invasive alien plant, Acacia nilotica

This paper describes a process-based metapopulation dynamics and phenology model of prickly acacia, Acacia nilotica, an invasive alien species in Australia. The model, SPAnDX, describes the interactions between riparian and upland sub-populations of A. nilotica within livestock paddocks, including the effects of extrinsic factors such as temperature, soil moisture availability and atmospheric concentrations of carbon dioxide. The model includes the effects of management events such as changing the livestock species or stocking rate, applying fire, and herbicide application. The predicted population behaviour of A. nilotica was sensitive to climate. Using 35 years daily weather datasets for five representative sites spanning the range of conditions that A. nilotica is found in Australia, the model predicted biomass levels that closely accord with expected values at each site. SPAnDX can be used as a decision-support tool in integrated weed management, and to explore the sensitivity of cultural management practices to climate change throughout the range of A. nilotica. The cohort-based DYMEX modelling package used to build and run SPAnDX provided several advantages over more traditional population modelling approaches (e.g. an appropriate specific formalism (discrete time, cohort-based, process-oriented), user-friendly graphical environment, extensible library of reusable components, and useful and flexible input/output support framework). (C) 2003 Published by Elsevier Science B.V.

Surface diffusion of strongly adsorbing vapors in activated carbon by a differential permeation method

Conventional methods to determine surface diffusion of adsorbed molecules are proven to be inadequate for strongly adsorbing vapors on activated carbon. Knudsen diffusion permeability (B-k) for strongly adsorbing vapors cannot be directly estimated from that of inert gases such as helium. In this paper three models are considered to elucidate the mechanism of surface diffusion in activated carbon. The transport mechanism in all three models is a combination of Knudsen diffusion, viscous flow and surface diffusion. The collision reflection factor f (which is the fraction of molecules undergoing collision to the solid surface over reflection from the surface) of the Knudsen diffusivity is assumed to be a function of loading. It was found to be 1.79 in the limit of zero loading, and decreases as loading increases. The surface diffusion permeability increases sharply at very low pressures and then starts to decrease after it has reached a maximum (B(mum)s) at a threshold pressure. The initial rapid increase in the total permeability is mainly attributed to surface diffusion. Interestingly the B(mum)s for all adsorbates appear at the same volumetric adsorbed phase concentration, suggesting that the volume of adsorbed molecules may play an important role in the surface diffusion mechanism in activated carbon. (C) 2003 Elsevier Ltd. All rights reserved.

Dehydration converts DsbG crystal diffraction from low to high resolution

Diffraction quality crystals are essential for crystallographic studies of protein structure, and the production of poorly diffracting crystals is often regarded as a dead end in the process. Here we show a dramatic improvement of poorly diffracting DsbG crystals allowing high-resolution diffraction data measurement. Before dehydration, the crystals are fragile and the diffraction pattern is streaky, extending to 10 Angstrom resolution. After dehydration, there is a spectacular improvement, with the diffraction pattern extending to 2 Angstrom resolution. This and other recent results show that dehydration is a simple, rapid, and inexpensive approach to convert poor quality crystals into diffraction quality crystals.

Avaliação da adsorção do herbicida 2,4-D em carvão ativado em pó utilizando água com diferentes qualidades

O 2,4-diclorofenoxiacético (2,4-D) é um dos herbicidas mais consumidos no Brasil e é preferencialmente usado devido a sua boa seletividade e baixo custo. Possui alta toxidade e baixa biodegradabilidade, oferecendo risco à saúde humana e ao meio ambiente, podendo ser encontrado em solos, águas superficiais e subterrâneas. Estudos mostram que o tratamento convencional da água possui baixa eficácia na remoção de microcontaminantes, com isso várias técnicas têm sido utilizadas na remoção de compostos em água, como a adsorção por carvão ativado. Apresenta-se a adsorção em carvão ativado tem se demonstrado como tecnologia eficiente na remoção de diversos contaminantes, dentre eles os agrotóxicos. Assim, o presente trabalho objetivou avaliar a adsorção do 2,4-D por três carvões ativados em pó (CAP) em água ultrapura e em água bruta do Rio Santa Maria da Vitória. A quantificação do herbicida foi analisada por cromatografia líquida de alta eficiência, após concentração da amostra pelo método de extração em fase sólida. Os ensaios de adsorção foram realizados com carvões ativados derivados da casca de coco (CAP-01), pinus (CAP-02) e palha de café (CAP-03), que foram caracterizados e avaliados na sua capacidade de remoção do 2,4-D nas duas matrizes de água. Dois modelos de isoterma de adsorção, Langmuir e Freundlich, foram aplicados para descrever os dados de adsorção, que indicaram o CAP-02 como o carvão que apresentou a melhor capacidade de adsorção do 2,4-D entre os carvões estudados, tanto em água ultrapura quanto em água bruta. Nos ensaios realizados em água bruta, houve redução da adsorção do 2,4-D para as três amostras de CAP, quando comparado com os ensaios realizados em água ultrapura, indicando interferência de compostos, como a matéria orgânica, no processo de adsorção.

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels

The influence of the dispersion of vapor grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/epoxy composites has been studied. A homogeneous dispersion of the VGCNF does not imply better electrical properties. The presence of well distributed clusters appears to be a key factor for increasing composite conductivity. It is also shown that the main conduction mechanism has an ionic nature for concentrations below the percolation threshold, while above the percolation threshold it is dominated by hopping between the fillers. Finally, using the granular system theory it is possible to explain the origin of conduction at low temperatures.

Carbon Nanofiber Type and Content Dependence of the Physical Properties of Carbon Nanofiber Reinforced Polypropylene Composites

The variation of the physical properties of four differ- ent carbon nanofibers (CNFs), based-polymer nano- composites incorporated in the same polypropylene (PP) matrix by twin-screw extrusion process was investigated. Nanocomposites fabricated with CNFs with highly graphitic outer layer revealed electrical isolation-to-conducting behaviors as function of CNF’s content. Nanocomposites fabricated with CNFs with an outer layer consisting on a disordered pyro- litically stripped layer, in contrast, revealed better mechanical performance and enhanced thermal sta- bility. Further, CNF’s incorporation into the polymer increased the thermal stability and the degree of crystallinity of the polymer, independently on the filler content and type. In addition, dispersion of the CNFs’ clusters in PP was analyzed by transmitted light opti- cal microscopy, and grayscale analysis (GSA). The results showed a correlation between the filler concentration and the variance, a parameter which measures quantitatively the dispersion, for all composites. This method indicated a value of 1.4 vol% above which large clusters of CNFs cannot be dispersed effectively and as a consequence only slight changes in mechanical performance are observed. Finally, this study establishes that for tailoring the physical properties of CNF based-polymer nanocomposites, both adequate CNFs structure and content have to be chosen.

RF Receiver Front End for 28.5 GHz Applications on a 70 GHz F-T SiGe BiCMOS Process

This article presents the design and test of a receiver front end aimed at LMDS applications at 28.5 GHz. It presents a system-level design after which the receiver was designed. The receiver comprises an LNA, quadrature mixer and quadrature local oscillator. Experimental results at 24 GHz center frequency show a conversion voltage gain of 15 dB and conversion noise figure of 14 5 dB. The receiver operates from a 2 5 V power supply with a total current consumption of 31 mA.

CVD of CrO(2): Towards a lower temperature deposition process

The deposition of highly oriented a-axis CrO(2) films onto Al(2)O(3)(0001) by atmospheric pressure (AP)CVD at temperatures as low as 330 C is reported. Deposition rates strongly depend on the substrate temperature, whereas for film surface microstructures the dependence is mainly on film thickness. For the experimental conditions used in this work, CrO(2) growth kinetics are dominated by a surface reaction mechanism with an apparent activation energy of (121.0 +/- 4.3) kJ mol(-1). The magnitude and temperature dependence of the saturation magnetization, up to room temperature, is consistent with bulk measurements.

HTLV-I/II and blood donors: determinants associated with seropositivity in a low risk population

OBJECTIVE: Blood donors in Brazil have been routinely screened for HTLV-I/II since 1993. A study was performed to estimate the prevalence of HTLV-I/II infection in a low risk population and to better understand determinants associated with seropositivity. METHODS: HTLV-I/II seropositive (n=135), indeterminate (n=167) and seronegative blood donors (n=116) were enrolled in an open prevalence prospective cohort study. A cross-sectional epidemiological study of positive, indeterminate and seronegative HTLV-I/II subjects was conducted to assess behavioral and environmental risk factors for seropositivity. HTLV-I/II serological status was confirmed using enzyme-linked immunosorbent assay (EIA) and Western blot (WB). RESULTS: The three groups were not homogeneous. HTLV-I/II seropositivity was associated to past blood transfusion and years of schooling, a marker of socioeconomic status, and use of non-intravenous illegal drugs. CONCLUSIONS: The study results reinforce the importance of continuous monitoring and improvement of blood donor selection process.